Hemodialysis and other forms of extracorporeal blood treatment require the removal of blood from a patient by means of an arterial set, passing of the blood to a blood processing device such as a dialyzer, and returning of the blood to the patient again through a venous blood set.
Maintenance of a good blood set access is a major cost of dialysis, which is the most common extracorporeal blood treatment, although other types of blood treatment are also used, for example passing of the blood through an absorption bed for removal of toxins and the like, hemoperfusion, and other forms of blood treatment.
Beyond the initial cost of the surgical procedure to establish a fistula or graft in the patient, the keeping of adequate blood flow in a modified peripheral blood vessel of the patient frequently involves secondary surgical intervention for reconstruction of an old blood vessel site on the patient. Alternatively, it may be necessary to establish an entirely new fistula or graft at a new site if the old one fails.
Failure is evidenced typically by stenosis of the blood vessel, or blockage of an implanted catheter or other venous access site, with a consequent reduction in blood flow that eventually shuts down the site.
If site failure is detected early enough, a less invasive technique such as balloon angioplasty can be employed to open the stenosis at a greatly reduced cost. Early detection of stenosis can be measured by rise in pressure in the blood vessel or implant that reflects a restriction beginning to form downstream. The technique described in Omachi U.S. Pat. No. 5,454,374 has been used to measure the baseline pressure access site for early detection of such a pressure rise. Another method used by clinicians is to measure recirculation in the vessel during dialysis. As the flow is restricted at the point of access, the blood pumping rate indicated on the dialysis machine may exceed the flow rate of fresh blood coming into the vessel, so that some is recirculated from the venous access site to the arterial access site in the patient. This leads to inadequate dialysis since already cleansed blood is thus being reprocessed.
Various methods for measuring the degree of recirculation of this type are known. Another method described by Krivitsky determines blood flow in the access as a marker for stenosis. In this method blood set flow and recirculation is determined with arterial and venous flow reversed between the arterial and venous access sites, which are typically fistula needles which enter the vein. In the prior art, clinicians typically accomplish this by stopping the flow of blood, clamping off all the lines, disconnecting the set or sets from the fistula needles, and then reconnecting the arterial line to the venous fistula while connecting the venous line to the arterial fistula.
Also regarding catheters (which are typically connected to larger veins or even the vena cava) it is known that catheter blockage may be relieved by reversing flow.
By this invention, a flow set is provided for the communication of blood between a patient and a blood processing device in which the flow restriction at a patient access site can be easily monitored without any external disconnection of the connections needed for the normal flow of blood from a patient to a blood processing device such as a dialyzer, and then from the dialyzer back to the patient. Thus, a great improvement in the convenience of use of the tubular set of this invention is provided. Also, breaks in sterility are avoided, since there is no need to make external disconnections in order to test the patency of a patient access site. Also, the tubular set of this invention can be a combined arterial and venous set, while, most often in the prior art, a separate arterial set and a separate venous set are used. This provides convenience of use through the unification of the set.
Also, catheters which are implanted in the venous system of a patient for dialysis access or the like may develop a "fibrin sheath" on the outside of the catheter within the blood vessel, for example the jugular or subclavian veins or the vena cava. This fibrin sheath coats the outside of the catheter and can extend over the end thereof.
At the outflow port, this is generally not too serious a problem since the outflowing blood forces the fibrin sheath open easily. However, at the inflow port of the catheter, the sheath can act as a one way valve, collapsing with increasing negative pressure to seriously interfere with flow through the catheter.
Upon such an occurrence, by this invention, the blood flow through such a blood access catheter can be reversed for continuation of a desired medical procedure such as hemodialysis.